The present invention relates to the use or specific (per)fluporopolyether compounds for improving the surface hydro- and oil-repellence properties of substrata having a low surface energy, i.e. substrata which are per se wettable with difficulty both by water and by hydrocarbons and which are desired to be still less wettable. This lower wettability can for example be usefully utilized to increase the resistance to penetration of liquids (for example water or hydrocarbons) in membranes or in porous septa formed by substrata having a low surface energy, such as for example fluoropolymers, in particular polytetrafluoroethylene (PTFE).
With substrata having a low surface energy, all the surfaces with critical wetting tension lower then 40 mN/meter generally are meant; in particular fluorinated polymers, for example PTFE, belong to this class.
It is known in the prior art that materials having a low surface energy are used in the preparation of porous and non porous membranes, used for example to separate gaseous mixtures or for the filtration of liquids/gases. For these uses an improved resistance of the membranes to wettability and to penetration of liquids, both of aqueous and hydrocarbon type, is required. It is known the treatment of surfaces by (per)fluoropolyethers having non reactive end groups, in particular of perfluoroalkyl type. Said treatment leads to a lower wettability, however it shows the drawback of an insufficient permanence of the treatment effects, due to the easy migration and/or removal of the treating agent.
The Applicant has surprisingly and unexpectedly found that this technical problem can be solved by using particular (per)fluoropolyethers as defined hereinafter.
An object of the present invention is the use for improving the surface hydro- and oil-repellence properties of substrata with a low surface energy having a critical wetting tension lower then 40 mN/meter, of (per)fluoropolyether mono- and bifunctional derivatives having the following structures:
Wxe2x80x94Lxe2x80x94YFCxe2x80x94Oxe2x80x94Rfxe2x80x94CFYxe2x80x94Lxe2x80x94Wxe2x80x83xe2x80x83(I)
Rfxe2x80x94CFYxe2x80x94Lxe2x80x94Wxe2x80x83xe2x80x83(II)
wherein:
L is a linking organic group xe2x80x94COxe2x80x94NRxe2x80x2xe2x80x94(CH2)qxe2x80x94, with Rxe2x80x2xe2x95x90H or C1-C4 alkyl; q is an integer comprised between 1 and 8, preferably 1-3;
Yxe2x95x90F, CF3;
W is a xe2x80x94Si(R1)xcex1(OR2)3-xcex1 group with xcex1=0,1,2, preferably xcex1=0,1;
R1 and R2 equal to or different from each other are C1-C6 alkyl groups, optionally containing one or more ehter O, C6-C10 aryl groups, C7-C12 alkyl-aryls or aryl-alkyls;
Rf has a number average molecular weight in the range 200-5,000, preferably 300-2,000 and it comprises repeating units having at least one of the following structures, statistically placed along the chain:
(CFXO), (CF2CF2O), (CF(CF3)CF2O), (CF2CF(CF3)O),
wherein
Xxe2x95x90F, CF3;
In particular Rf can have one of the following structures:
1) xe2x80x94(CF2O)a xe2x80x2xe2x80x94(CF2CF2O)bxe2x80x2xe2x80x94 with axe2x80x2/bxe2x80x2 comprised between 0.5 and 2, extremes included, axe2x80x2 and bxe2x80x2 being integers such to give the above mentioned molecular weight;
2) xe2x80x94(C3F6O)rxe2x80x94(C2F4O)bxe2x80x94(CFXO)txe2x80x94 with r/b=0.5-2.0; (r+b)/t is in the range 10-30, b, r and t being integers such as to give the above mentioned molecular weight, X has the above indicated meaning;
3) xe2x80x94(C3F6O)rxe2x80x2xe2x80x94(CFXO)txe2x80x2xe2x80x94 txe2x80x2 can be 0;
when txe2x80x2 is different from 0 then rxe2x80x2/txe2x80x2=10-30, rxe2x80x2 and txe2x80x2 being integers such to give the above mentioned molecular weight; X has the above indicated meaning;
In the above mentioned formulas:
xe2x80x94(C3F6O)xe2x80x94 can represent units of formula
xe2x80x94(CF(CF3)CF2O)xe2x80x94 and/or xe2x80x94(CF2xe2x80x94CF(CF3)O)xe2x80x94
In structure (II) wherein Rf is monofunctional, the other end group is of Txe2x80x94Oxe2x80x94 type, wherein T is a (per)fluoroalkyl group selected from: xe2x80x94CF3, xe2x80x94C2F5, xe2x80x94C3F7, xe2x80x94CF2Cl, xe2x80x94C2F4Cl, xe2x80x94C3F6Cl; optionally one or two F atoms, preferably one, can be replaced by H.
Also mixtures of the above mentioned compounds (I) and (II) can be used. Ratios by weight between the compounds (I) and (II) in the range 100:0 and 5:95 can generally be used.
As (per)fluoropolyether compounds of structure (I) and (II), those wherein Rf has structure (3) are preferably used in the present invention. It has been unexpectedly found that improved hydro- and oil-repellence values are obtained when the compounds of formula (I) with Rf having structure (3) are used. Mixtures of these preferred compounds (I) and (II) with Rf of structure (3) can be used.
As said, with substrata having a low surface energy, all the surfaces having a critical wetting tension lower than 40 mN/meter are generally meant. In particular fluorinated polymers, for example PTFE belong to this class. Other examples of substrata having a low surface energy are polyolefins, for example polyethylyne, polypropylene, polyolefine elastomers, thermoplastic copolymers of tetrafluoroethylene, thermoplastic homopolymers and copolymers of vinylidenfluoride or of chlorotrifluoroethylene, etc.
The bifunctional fluoropolyethers of formula (I) are obtainable by well known processes in the prior art, see for example the following patents herein incorporated by reference: U.S. Pat. No. 3,847,978 and EP 374,740 for the preparation of compounds having acid end groups of xe2x80x94COF type. The silane end group of formula (I) can be obtained by transformation of the xe2x80x94COF into ester xe2x80x94COOR wherein R=alkyl, preferably C1-C12, and subsequent ester reaction according to the processes for example mentioned in U.S. Pat. No. 3,810,874. In particular, see U.S. Pat. Nos. 5,714,637, 4,094,911, 4,818,619. To increase the content of bifunctional acid compounds the keto-acid described in U.S. Pat. No. 3,847,978 can be treated with bases obtaining a mixture of carboxylic acids and polyethers having xe2x80x94CF2H end groups. When the pure bifunctional derivative of formula (I) is desired to be obtained, further purification steps, for example distillation or chromatography can be carried out.
The monofunctional compounds of formula (II) are obtainable according to the methods mentioned in EP 374,740, and subsequent transformation of the xe2x80x94COF groups into silane end groups according to the same methods above mentioned for the bifunctional compounds of formula (I).
The (per)fluoropolyethers of the invention can be easily applied on the surface substrata by brushing, spraying, padding, using formulations comprising water and/or solvents having a low environmental impact.
The (per)fluoropolyether derivatives of the invention can be formulated in formulations comprising solvents or water/solvent mixtures. Preferably polar solvents, or mixtures thereof, suitable to the purpose can be selected from the following classes: aliphatic alcohols having from 1 to 6 carbon atoms; aliphatic glycols having from 2 to 8 carbon atoms, optionally having an esterified hydroxyl; ketones or esters having from 3 to 10 carbon atoms, etc. Solvent/water mixtures, such as for example ketone/water or alcohol/water mixtures in ratios by volume between 10:90 and 90:10 can also be used.
In the above mentioned formulations the concentration of the (per)fluoropolyethers of formula (I) and (II) is generally in the range 0.1-30% by weight with an amount of (per)fluoropolyether compound applied to the substratum surface in the range 0.1-20 g/m2, depending on the porosity of the treated material.
To obtain the best results, it is preferable that the polar solvent is combined with a small amount of water, generally between 100 ppm and 10% by weight, optionally in the presence of a silanization catalyst. Alternatively, a thermal treatment cycle can be used in order to favour the crosslinking of the applied compound of structure (I) or (II).
To facilitate the removal of the solvent present in the porosities after the application of the formulations comprising the invention compounds of structure (I) and (II), an additional thermal treatment of the treated surface can follow at a temperature in the range 60-150xc2x0 C.
The present invention will be better illustrated by the following Examples, which have a merely indicative but not limitative purpose of the scope of the invention itself.